Ignition coil assembly with extension for electrical connection of an ignition plug of an endothermic engine,—wherein said extension (10) comprises an essentially tubular hollow body (11), which is secured to a container containing the electrical/electronic means of the ignition coil for generation of high voltage electrical energy to transmit to an ignition plug for the triggering of sparks secured to the engine block of said engine,—wherein a first end area (10.1) of said tubular body is engaged, in a detachable manner, on the free end of said ignition plug, and—wherein electrical connection means (10.26, 20, 10.36), provided for the transmission of high voltage electrical energy between said electrical/electronic means of the ignition coil and said ignition plug, are contained in said tubular body (11). According to the invention, said means for electrical connection (10.26, 20, 10.36) comprise at least one filter means (20) of the high frequency electromagnetic disturbances produced by the operation of said coil, wherein a winding of electrically conductive wire surrounds a central core (20.3) in ferromagnetic material dispersed in a polymer base.